(1) Field of the Invention
The present invention relates to a toner supply device and a developing unit using this, in particular relating to a toner supply device and a developing unit using this for use in an image forming apparatus for performing image formation with toner.
(2) Description of the Prior Art
Conventionally, in image forming apparatuses using toner, such as copiers, facsimile machines, etc., a toner supply device such as a toner cartridge etc., is used to supply toner to the developing unit to thereby achieve continuous operation of image output.
Examples of generally known methods for supplying toner to the developing unit include: a configuration in which toner stored in a toner cartridge is directly supplied to the developing unit (Patent document 1: see Japanese Patent Application Laid-open 2003-162143); and a configuration in which toner in a toner cartridge is supplied by a screw from a predetermined position to the developing unit (Patent document 2: see Japanese Patent Application Laid-open Hei 10-142936).
However, with the conventional method of directly supplying toner from the toner cartridge to the developing unit, the fluidity of the supplied toner is prone to vary, resulting in a cause of variations in image quality.
Also, in a case where fluidity of toner is improved by taking measures so that even toner which has been degraded in fluidity due to long-term inactivity or the like can be supplied without hindrance, toner beyond a controlled amount may be supplied to the developing unit, causing the problem that the toner concentration in the developer rises, exerting influence on image quality and color tones.
On the other hand, in a system in which toner is conveyed and supplied by use of a screw, in order to convey a large amount of toner to support high-speed printing, it has been necessary to enlarge the toner cartridge body so that load will not be applied to the screw. This presents the problem in that the ratio of the amount of stored toner to the interior volume of the toner cartridge becomes small.
To deal with this, as a method of conveying toner stored in a toner cartridge, there is a technique by which toner is conveyed to a predetermined position by rotating the toner cartridge itself instead of using a screw (see Patent document 3: Japanese Patent Application Laid-open Hei 7-20705, Patent document 4: Japanese Patent Application Laid-open Hei 8-339115, and Patent document 5: Japanese Patent Application Laid-open Hei 6-348127).
In accordance with this system, since toner is conveyed by rotating the toner cartridge itself, it is not necessary to provide a screw for toner conveyance inside the toner cartridge. Accordingly, it is not necessary to consider the load on the screw when toner is conveyed, so that it is possible to increase the ratio of toner stored in the toner cartridge.
However, since in the above-mentioned prior art, toner is directly discharged from the toner cartridge, it is difficult to stably convey the toner depending on the amount of toner stored in the toner cartridge, the rotational rate of the toner cartridge and other factors, hence there occurs the problem that toner cannot be supplied to the developing unit in a stable manner.
To avoid this, a toner supply device having a toner feed device that is adapted to temporarily store the toner having been conveyed and discharged from the toner cartridge and deliver it to the developing unit (see Patent document 6: Japanese Patent Application Laid-open No. 2004-317592) has been disclosed. This manipulation, even when it has such a configuration that toner is conveyance and discharged by rotating the toner cartridge body, makes it possible to stably supply the toner discharged from the toner cartridge to the developing unit by use of the toner feed device.
Yet, since the aforementioned conventional system is constructed of a number of components including a toner cartridge, a toner feed device, a toner input portion for forwarding toner to the developing unit, etc., there are the structural complexity problem and the problem that toner clogs in the toner conveyance path.